Without a drought

Posted by Adolph Rosekrans on January 15, 2017

It's been wonderfully wet in northern and central California this year. (The 2017 "water year" started on October 1.)

Many media outlets have declared the "drought" to be over. That is generally true in many respects, but it doesn't mean all of California's cities, farms, rivers and wetlands will be provided ample supplies in 2017 or thereafter.

San Francisco's extensive surface storage system in the Tuolumne River watershed will certainly fill to its capacity of about 1,230,000 acre-feet in 2017 - 360,000 acre-feet in Hetch Hetchy Reservoir, 300,000 acre-feet in Cherry and Eleanor Reservoirs, and at least 570,000 acre-feet in its water bank in Don Pedro Reservoir.

San Francisco's water bank in Don Pedro can hold up to 740,000 acre-feet after the flood control season. San Francisco relies on this storage as part of its supply, but the reservoir is owned and operated by the Turlock and Modesto Irrigation Districts.

Flood Control Operations at Don Pedro Reservoir

Don Pedro Reservoir's total storage capacity is 2,030,000 acre-feet, but flood control requirements allow only 1,690,000 of water to be stored during winter and spring runoff months. High inflow during early January storms brought the storage level to more than 1,800,000 acre-feet, so reservoir managers will be "spilling" water to bring the storage level down over coming weeks. The river channel downstream in Modesto can accommodate only about 16,000 acre-feet per day without flooding parts of the city.

Early season storms have already filled most of California's on-stream reservoirs to their permitted capacity. Only New Melones Reservoir on the Stanislaus River, which can hold more than twice the river's average annual flow, is uncertain of filling in 2017.

Further, in areas of the Central Valley where agreements between landowners and water agencies are in place, 2017 will provide substantial opportunity to recharge depleted groundwater basins.

California's water supply does not depend solely on rain and snow in the Central Valley watershed. Southern California gets about 5,000,000 acre-feet (14 times the volume of Hetch Hetchy Reservoir) annually from the Colorado River. Fortunately, early season storms have reached the Rocky Mountains, which bodes well for Colorado River in 2017. But most hydrologists agree that the Colorado does not have enough flow to deliver current levels of supplies over the long-term, as evidenced by the steady decline of storage at Lakes Mead and Powell (which when full 30 years ago held close to 50,000,000 acre-feet). If southern California receives less water from the Colorado, it may seek additional supplies from the Central Valley and Bay-Delta watershed.

And battles over limited water supplies in the Central Valley and Bay-Delta continue on many fronts, including:

The State Water Board is presently considering substantial increases in required flow into the Delta from the southern side, drawing praise from Delta interests, environmentalists and fishermen, but intense opposition from local water agencies, including the Turlock and Modesto Irrigation Districts with whom San Francisco shares the Tuolumne River.

Controversial "drought" legislation, passed by Congress in December as part of the Water Resources Development Act, threatens application of the Endangered Species Act to protect salmon and Delta smelt.

The State Water Board will soon hold hearings on the "California WaterFix" - the controversial proposal, originally known as the Peripheral Canal, to bring water from north to south in California while bypassing the Delta.

Our campaign to restore Yosemite's Hetch Hetchy Valley is largely, but not entirely, separate from these other major ongoing battles. We don't begrudge San Francisco a reasonable supply of water from the Tuolumne River - we respect the State Board's ongoing process to determine how much water should remain instream and how much can be diverted for urban and agricultural use.

We only ask that San Francisco remove its water storage from Yosemite's Hetch Hetchy Valley. We are confident it can do so under any prevailing hydrologic conditions - with or without a drought.